Far East Federal University, Vladivostok, Russia:

B. G. Tarasov, Professor, Doctor of Engineering Sciences, bgtaras@gmail.com

This article is devoted to the earlier unknown fracture mechanism (fan mechanism) which governs propagation of shear fractures and anomalous properties of rocks. It should be mentioned that these properties appear anomalous as they have not been yet discovered experimentally. In reality, these fundamental properties of strong rocks show themselves under conditions of seismic depths. The specific structure of dynamic cracks is composed by an echelon of slabs created by inclined tensile cracks ahead of a running shear fracture. The conditions of such structure are disclosed. It is shown that under high lateral pressures, the slabs can rotate under shear displacement of fracture surfaces and act as pivots forming a fan structure representing the fracture head. The fan structure possesses some unique properties, in particular, nearly zero shear resistance, and creates high concentration of shear stresses at the shear fracture tip, which ensures growth of the fracture in solid rocks subjected to anomalously low shear stresses. Propagation of such fractures is accompanied by anomalously low energy of failure, which makes rocks super brittle.
The study was supported by the Ministry of Science and Higher Education of the Russian Federation, Grant No. RFMEFI58418X0034.

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